A Frequency Diversity Pulse-Pair Algorithm For Extending Doppler Radar Velocity Nyquist Range

Millimeter wave radars have been widely used for atmospheric remote sensing and tracking hard-targets from airborne platforms. For these radars, the product of the unambiguous range and Doppler velocity is limited by the radar wavelength. This work focuses on a novel method to extend the Nyquist rate of millemeter radars, which uses frequency diversity pulse-pairs for Doppler phase estimation. Two short pulses with center-frequencies of f(1) followed by f(2) are transmitted during the first pulse repetition interval (PRI). During the next PRI, the pulses transmitted are in the order f(2) followed by f(1) respectively. There are two mechanisms for error reduction. First, the "beat" phases of the f(1)/f(2) and f(2)/f(1) pairs cancel out in the expected value sense. Second, since the f(1)/f(2) and f(2)/f(1) phase estimates are highly anti-correlated, the sum of the two phase estimates has a much smaller variance than the individual phase estimates. Based on Monte-Carlo simulations, the feasibility of this method is demonstrated herein. Ongoing data analysis is discussed.